C＃HttpWebRequest缓存

Question

在我的应用程序中，我构建了一个GET请求，只要内容与服务器上的内容相同，就会从缓存中返回响应。

            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Method = "GET";                
            request.ReadWriteTimeout = 2000;
            request.KeepAlive = true;
            request.AutomaticDecompression = DecompressionMethods.GZip;

            request.CachePolicy = new HttpRequestCachePolicy(HttpRequestCacheLevel.Revalidate);
            request.Host = host;
            request.Referer = referer;
            request.UserAgent = ua;

            request.Accept = "text/javascript, text/html, application/xml, text/xml, */*";
            request.ContentType = "application/json; charset=UTF-8";
            request.Headers.Add("Accept-Ranges", "bytes");
            request.Headers.Add("Accept-Encoding", "gzip, deflate, sdch");
            request.Headers.Add("Accept-Language", "en-US,en;q=0.8,en-US;q=0.5,en;q=0.3");

            using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
            {
                if (response.StatusCode == HttpStatusCode.OK)
                {
                        using (var stream = new StreamReader(response.GetResponseStream()))
                        {
                            content = stream.ReadToEnd();
                        }
                }
                else content = string.Empty;
            }

但是request.GetResponse().IsFromCache总是返回false，即使内容相同（我仍然可以使用StreamReader成功读取它）。 当我在浏览器中连续执行相同的两个请求时，它会成功缓存。 我已经尝试了所有可能的缓存策略。谁能解释我做错了什么？